ABC's three-hour "Closeup" on "Growing Old in America" is something that should be required viewing for every American under the age of 60.

But there probably ought to be some kind of reverse PG rating system to warn off anybody older than 60, or anyone who is contemplating retirement in the next few years.

That is because this intense and massive production, tonight at 8 on Channel 7, is, above all, depressing, especially so for those who are already part of America's aged and those who are about to be.

It is important, yes. And well and carefully reported and produced. It is, by and large, interesting and informative. But it is also heartbreaking, wrenching, enraging and frustrating.

We are, warns host and narrator Hugh Downs, "critically unprepared" for the crisis of an aging society. Yet, by the year 2000, one in every five Americans will be over 65 with a life expectancy of another 20 years and most of life's grueling health problems yet to be overcome.

According to former Health, Education and Welfare now Health and Human Services secretary Joseph Califano, "By the year 2020, at the rate we're going and the way resources are now allocated, 65 percent of the federal budget will go to people over 65 years of age. That's how much they're going to need. That's veteran payments, that's disability tax payments, that's Social Security payments, that's health care payments. Now we've got to plan for that."

But the thesis of ABC's three hours is that, in fact, practically nobody is planning for anything.

The report on aging is divided into three segments: Retirement, Health Care and Long Term Care. Each segment is discrete, but each fits neatly into the next. If there is one standout, it is the middle segment, on the health-care crisis for the increasing ranks of the elderly.

That crisis is the combined result of misperception -- the myth that "to be old is to be sick, sexless and senile" -- along with lack of funds, lack of caring.

Take the problem, as does ABC, of Benjamin Tyler:

"Benjamin Tyler, 91, retired farmer, was admitted to a hospital in Colorado with a hip fracture. A bladder catheter was inserted, which caused an infection. He became totally disoriented and was labeled as having Alzheimer's dementia. Placed on physical restraints and heavily sedated, he finally was seen by Dr. Dennis Jahnigen, director of geriatrics at the VA Hospital in Denver."

Tyler was lucky, because Jahnigen quickly spotted the problem -- we see part of the interview with Jahnigen and hear Jahnigen say, "It turned out that he was not demented at all, but was suffering from the effects of, number one, the infection, and also from the effects of some of the medications which were given to calm him down."

When his eight or nine medications were cut back to one or two, his infection was treated and his mind cleared.

Dr. Gene Cohen, director of the program on aging for the National Institute of Mental Health, underlines the Tyler case for ABC with this statistic: ". . . in a hospital setting where the approach is much more rigorous, the degree of misdiagnosis can still be somewhere in the 15 to 30 percent range. In the community, sometimes the diagnosis can be as high as 50 percent inaccuracy."

At least part of the reason for this is the shortage of doctors for the elderly.

Notes the narrator, "Underlying all these problems, a more fundamental problem: a medical community largely untrained and uninterested in treating elderly patients. In only a few years, our nation will need more than 10 times our current number of geriatricians -- a specialty, though, regarded by many doctors as too difficult; unprofitable."

A doctor agrees: "The reality is that a surgeon can go in and do . . . a 15-minute procedure, like a cataract, and bill for $1,500 to $5,000, depending on the region they live in, and be there 15 minutes, whereas a busy family practitioner or internist taking care of old people can go in and spend . . . 30, 40, 50 minutes, a whole hour, trying to evaluate them, and be able to bill 30 bucks . . ."

Confirms Dr. Jahnigen, "The truth is that the reimbursement scheme, to a large degree, drives what is done in medicine."

But cuts in Medicare and Medicaid payments and the recent institution of the already infamous DRGs -- diagnosis-related groups -- have turned reimbursement into the kind of cruel hoax that drives patients to do things like taking only half a pill, instead of the prescribed number, to make them last longer.

Under the DRG system, devised to prevent overlong hospital stays, each procedure is assigned a number of days for which Medicare will pay the hospital a flat sum. If the Medicare patient is hospitalized longer, the hospital pays. This has resulted in the release of patients even though they were too sick to leave, because they used up their DRGs. ABC found one foreign-owned hospital chain in California that offers an additional incentive to its doctors to get the patients out in a hurry. If, for example, a 10-day DRG patient is discharged in eight days, the excess fee -- already paid for the last two days -- is shared with the doctor.

The other two parts of "Growing Old in America" are similarly bleak. The first, for example, reports that even though corporate pension funds, with their tax breaks, amount to $1 trillion, half of American workers have no pension coverage; women are especially hard hit.

And the last, on long-term care, deals with the ultimate catastrophe, because with illnesses like Alzheimer's, strokes and other long-term degenerative illnesses, practically no insurance or health plan provides coverage.

There are a few hopeful spots in the vast problem, but these are, as one expert notes, mere "candles flickering in the darkness." The ABC "Closeup" is another candle.